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United States Patent |
5,170,691
|
Baatrup
|
December 15, 1992
|
Fluid pressure amplifier
Abstract
A continually operating fluid pressure amplifier having a reciprocating
piston system comprising a broad low pressure piston and a narrow high
pressure piston, of which the latter, together with its piston cylinder,
is arranged as a three-way pilot valve for operating a bistable control
valve that controls the reciprocation of the piston system. The control
valve has a primary valve slide controlling the said reciprocation and an
auxiliary slide operable to open and close relevant conduit connections
for initial amplification of the shift control signals governing the
operation of the control valve, whereby a very safe operation of the
entire system is ensured. Also ensured is a rapid return stroking of the
piston system, such that the produced high pressure can be maintained
substantially constant.
Inventors:
|
Baatrup; Johannes V. (Henrik Ibsensvej 7, DK-6400 Sonderborg, DK)
|
Appl. No.:
|
567784 |
Filed:
|
August 15, 1990 |
Current U.S. Class: |
91/287; 91/290; 91/319; 91/321; 417/403 |
Intern'l Class: |
F01L 025/02 |
Field of Search: |
60/563,593
91/287,290,319,321,417
417/325,403
137/596.18
|
References Cited
U.S. Patent Documents
2583285 | Jan., 1952 | Zehnder | 91/290.
|
2722233 | Nov., 1955 | Schneck | 137/596.
|
2722946 | Nov., 1955 | Mueller | 137/596.
|
3863672 | Feb., 1975 | Theriot et al. | 137/596.
|
4509330 | Apr., 1985 | Zimber et al. | 60/563.
|
4864914 | Sep., 1989 | LeMoine | 60/563.
|
Foreign Patent Documents |
1276629 | Jun., 1972 | GB | 417/403.
|
Primary Examiner: Look; Edward K.
Assistant Examiner: Nguyen; Hoang
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus
Claims
I claim:
1. A differential single-acting fluid pressure amplifier comprising:
a piston system including a first large diameter piston disposed in a large
diameter cylinder portion and a second narrow diameter piston disposed in
a narrow cylinder portion adjacent said large diameter cylinder portion, a
medium pressure chamber defined at a free end of said first piston, a high
pressure chamber defined at a free side of said second piston, a low
pressure chamber defined between said first and second pistons, a medium
pressure inlet connected to a medium pressure fluid source, a low pressure
outlet for connecting a return conduit to said medium pressure fluid
source, suction valve means for connecting said medium pressure inlet to
said high pressure chamber, said low pressure outlet being connected with
said low pressure chamber, an automatically controlled switching valve
means for alternatingly connecting said medium pressure chamber with said
medium pressure inlet and said low pressure outlet, said switching valve
means including a primary switch valve member shiftable in one direction
by an applied medium pressure and in an opposite direction by action of a
return spring upon removal of said medium pressure, a pilot system for
applying and removing said applied medium pressure, said pilot system
including a pipe connected to an orifice in a wall of the narrow cylinder
portion and located so as to be disposed in front of the second piston
when the second piston assumes a retracted position in the narrow cylinder
portion, whereby the orifice is connected with the medium pressure inlet
through said suction valve means, and behind the second piston when the
second piston assumes a foremost position in the narrow cylinder portion,
whereby the orifice is connected with said low pressure chamber thereby
enabling removal of the applied medium pressure from the switch valve
member in order to enable the same to be switched by the action of the
return spring to a position in which the medium pressure chamber is
connected with the low pressure outlet for effecting return movement of
the piston system, wherein said switch valve member, when connected with
the pressure medium pressure inlet in the retracted position of the piston
is caused by the applied medium pressure overcoming the action of said
return spring to switch to a position in which the medium pressure chamber
is connected with the medium pressure inlet for effecting a working stroke
of the piston system, and wherein means are provided for ensuring that the
switch valve member, by each successive shift, is fully shifted between
two opposed end positions including an auxiliary switch valve member
operatively connected with said primary switch valve member so as to be
movable therewith, said auxiliary switch valve member having a limited
displacement relative to said switch valve member in response to the
primary switch valve member reaching the respective end positions such
that the auxiliary valve member, at each shift, is thereafter displaced
further by one of the applied medium pressure and the action of the return
spring, wherein the auxiliary valve member and the pressure switch valve
member are constructed such that in the initial phase of each shifting
movement, the auxiliary switch valve member and the primary switch valve
member establish a direct connection between the pilot system and an
associated shift controlling source including one of the medium pressure
source and a low pressure source, while, by the mutual displacement of the
auxiliary switch valve member and the pressure switch valve member at the
end of each shifting operation, a channel for establishing said direct
connection is closed internally, while at the same time a corresponding
channel for connection to the other pressure source is opened internally,
such that it is ready for immediate action by a following shift operation
of the valve members.
Description
FIELD OF THE INVENTION
The present invention relates to a pressure amplifier of the type
comprising a reciprocating piston system having a broad piston working in
a low pressure cylinder and a narrow piston working in a narrow cylinder,
whereby the introduction of a relatively low pressurized fluid into the
former cylinder will result in a displacement of the narrow piston in the
latter cylinder, such that a fluid in this cylinder can be discharged with
an increased pressure, though at a decreased rate of flow compared with
the flow introduced into the low pressure cylinder.
BACKGROUND OF THE INVENTION
Pressure amplifiers of this type are relatively simple compared with
devices for raising the pressure directly from zero to the required high
value, but for many applications it is a disturbing fact that the
oscillating motion of the amplifier piston system gives rise to
fluctuations of the high pressure as delivered from the amplifier. Of
course, the high pressure fluid is delivered through a check valve which
will prevent backflow to the low or medium pressure system, but if there
is a certain fluid consumption or leakage in the high pressure system a
pressure drop may well occur therein if the high pressurized fluid is not
fully constantly supplied from the pressure amplifier. Since the
amplification is a matter of reciprocating a piston system it will be
unavoidable that such pressure drops may occur, already because the piston
system has to stop its action whenever its direction of movement is being
inverted.
There is distinguished between single-acting and double-acting pressure
amplifiers, just as with piston pumps, and obviously a double-acting
device will be better suited to produce an almost constant discharge
pressure, because in a double-acting system there is no operational pause
connected with an idle return stroke of the piston system as in a
single-acting system. However, there may still be problems with respect to
a rapid and safe actuation of the means for cylically changing the
direction of movement of the piston system. For many applications it is a
major demand that the pressure amplifier should be of a small size and of
a low price, and for that reason the single-acting devices are preferred
for many purposes, e.g. for incorporation in various types of tools and
vehicles. When used e.g. in connection with hydraulic actuators for the
holding of workpieces being worked the pressure amplifiers should be able
to maintain the discharge pressure almost constant.
Still, however, the single-acting amplifiers show the drawback of a
relatively low effective working frequency due to the need of an idle
return stroke for each working stroke. This implies relatively large outer
dimensions for a given rate of high pressure flow, and pressure dives are
liable to occur at the high pressure side.
The U.S. Pat. No. 3,737,254 discloses such an amplifier and asserts that
the return switching is effected instantaneously, but since during the
switching phase the axial forces acting upon the switch controlling
mechanism are directed opposite the moving direction of the piston system,
and since the fluid from the low pressure cylinder chambers has to pass
through relatively long and narrow channels, the resulting working
frequency is bound to be relatively low anyway.
For simplicity the piston system should be reciprocated by the medium
pressure fluid, i.e. by the fluid moving the system through both its
working strokes and its return strokes, and also the associated switch
control should be effected by the medium pressure fluid. This invites to
the use of a simple slide controller, which is reversed, directly or
indirectly, in response to the piston system arriving at its respective
extreme positions, so as to thereby be operated to connect the relevant
piston chambers with the medium pressure source and a low pressure return
system in an alternating manner. However, such simple control systems are
well known to present some important operational problems, inter alia
because, for a really safe switching operation, they have to be provided
with some narrow channels, so-called nozzles, whereby the system is
vulnerable to a dirt blocking and is rather slow in its reactions.
Moreover the nozzles are subjected to wear, whereby after some time the
system may become unstable. These problems could be reduced with the use
of thicker valve channels, but that would give rise to problems with
respect to the safety of the switching operations and partly unexplainable
situations of equilibrium may occur, where the reciprocating piston system
just stops working.
It is known to stabilize the operation based on a mechanical snap locking
of the slide controller in its respective extreme positions, but this
implies increased costs and space requirements, and moreover the locking
system will be subjected to wear.
SUMMARY OF THE INVENTION
It is the primary purpose of this invention to provide a system of the type
referred to, which, with a simple modification, can be made to operate in
a reliable manner, with rapid control switch functions and rapid return
strokes of the piston system, and yet without any need of using mechanical
snap lock means or narrow nozzle passages in the control system.
According to the invention use is still made of the slide controller, which
has a first valve part member with bores connected with the medium
pressure source and the cylinder chambers of the respective opposite sides
of the said low pressure piston, respectively, and a second valve part
reciprocally slidably arranged relative to the first valve part and urged
by spring means towards a first end position, in which it establishes a
free flow connections between the connections to the cylinder chambers and
a blocking of fluid inlet from the medium pressure source, with the second
valve part being urgable by the medium pressure to an opposite, second end
position, in which it establishes a connection between the inlet of medium
pressure fluid and the cylinder chamber responsible for the working stroke
of the piston system, while blocking for the outlet from the opposite
cylinder chamber. The latter is permanently connected also to the low
pressure return system, such that the fluid in that chamber can easily
escape therefrom during the working stroke.
Further according to the invention the means for supplying the medium
pressure to the slide, i.e. the second valve member, are constituted by a
pilot connection to the high pressure cylinder portion at such a place
thereof which is uncovered by the high pressure piston in both of its
extreme positions, but otherwise closed by the piston, whereby after a
working stroke this connection will be open to the front side of the high
pressure piston and therewith directly to the medium pressure, while at
the end of each return stroke this particular connection will be open
towards the cylinder chamber portion connected with the low pressure
return system.
This will involve that the position of the second valve member will be
shifted towards its first end position by the action of the said spring
means, for example when the oppositely directed control pressure on the
second valve member is relieved at the end of the working stroke of the
piston system, while a shifting to the second end position is brought
about at the end of each return stroke of the piston system, when the
control pressure on the second valve member is increased towards the
applied medium pressure, thereby enabling the second valve member to be
displaced against the action of the spring means.
Still further according to the invention the second valve member cooperates
with an auxiliary slide, which moves along with the second valve member
except through the respective outermost partial distances, where the
auxiliary slide is held back by abutting respective opposed stop portions
of the first valve member, such that the mutual positions of the second
valve member and the auxiliary slide are shifted at the end of each
switching stroke. The auxiliary slide acts as a valve means between the
pilot connection and respective outlet and inlet means of the second valve
member, all in such a manner that at the end of a return stroke of the
piston system a very direct connection will be opened briefly between the
medium pressure source and the remote end of the pilot connection, i.e.
the end at which the pilot pressure acts upon the control valve system,
whereby extra security is obtained for the control valve system to
complete its shifting into the position in which it conditions an
operational switch over from return stroking to working stroking of the
piston system.
Although the last mentioned connection will be closed very soon after the
opening thereof, for example, during the very final phase of the movement
of the second valve member, it is nevertheless hereby ensured, by the
connection initially being fully open, that the valve shifting will take
place rapidly and with a high degree of safety.
At an opposite end of the control valve system the auxiliary slide is
operable to briefly open a connection between the remote end of the pilot
connection and the conduit leading to both the low pressure return system
and to the low pressure side of the piston system, before this connection
is broken by the very final motion of the second valve member towards its
respective end position. Hereby it is achieved that at the end of each
working stroke, when the piston system opens the pilot connection to the
fluid return system and thus enables the spring means of the slide
controller to shift the position of the second valve member, an additional
connection will be established directly between the pilot system and the
return system, whereby the pilot pressure is extra relievable for a safe
and fast return movement of the second valve member. Thus, the return
stroke of the piston system can be initiated in a reliable manner
immediately at the end of the working stroke.
During the final phase of the shifting the auxiliary slide will get stopped
so as to cause the auxiliary connection to be closed. Now it has served
its purpose, and it should of course not be open when, during the
following sequence, the pilot connection is opened to the medium pressure
system. By the same relative movement between the second valve member and
the auxiliary slide the connection at the first mentioned end of the
latter will be opened, but due to the displaced position of the second
valve member relative to the first valve member it will not be made
operative until this position is again changed, for example, as described
at the end of the return stroke of the piston system. In this manner the
internal connection can be opened preparatory to being brought into
operation, and there will be no difficulties with respect to the
alternating connection of the pilot system with the return system and the
medium pressure system, respectively. There will be no possibility of any
direct connection between the two latter systems at any time.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention is described in more detail with reference
to the drawing, wherein
FIG. 1 is a schematic diagram of a pressure amplifier system according to
the invention, while
FIGS. 2-5 are sectional views of a control unit therein.
DETAILED DESCRIPTION
In FIG. 1 is shown a unit 2 having an inlet 4 for a medium pressurized
fluid, which is passed through a pipe 6, a check valve 8, and a pipe 10 to
the top end of a high pressure cylinder 12, from which there is arranged a
high pressure outlet 14 through a check valve 16. The cylinder 12 is
mounted at the top of a wider low pressure cylinder 18 being connected at
the top and bottom with respective pipes or channels 20 and 22 connected
to a shift control unit 24. The pipe 20 has a branch 26 leading directly
to an outlet 28 connected with a return tank for the fluid.
The control unit 24 has a lower housing portion 30, which holds a
compression spring 32 and is connected, via a pipe 34, to the return pipe
26 and thus to the outlet 28. Also connected to the control unit 24 is a
branch 36 from the inlet pipe 6, while a pilot pipe 38 is connected to an
upper housing portion 40 of the unit. At its other end the pilot pipe 38
is connected to a stub 42 at the lower end of the high pressure cylinder
12.
The upper cylinder 12 has a piston 44 with upper end 46 and, lower end 48,
and through a connector rod or rather spacer rod 50 this piston is in
connection with a wider piston 52 in the lower cylinder 18. The cylinder
chamber above the piston 44 is designated 54, while the chamber underneath
the lower piston is designated 56 and the chamber between the two pistons
58. A compression spring 60 is mounted upstanding from the bottom of the
lower cylinder chamber 56 so as to be engageable by the lower side of the
piston 52. Alternatively this spring could be mounted depending from the
piston.
Controlled by the pressure in the pilot pipe 38, the control unit 24 is
shiftable between two connection modes as depicted graphically, for
example, one in which there is a direct connection between the pipes 20
and 22, while the inlet branch 36 is blocked, and one in which the inlet
branch 36 is connected to the pipe or channel 22.
Briefly, the system shown will operate in the following manner:
Fluid under medium pressure from the inlet 4 is introduced through the
parts 6, 8 and 10 into the upper cylinder chamber 54, whereby the piston
system 44,50,52 is forced downwardly. Governed by the spring 32 the
control unit 24 provides for a "return condition" as shown in the upper
half of the unit graph, i.e. in which the fluid can flow freely from the
lower cylinder chamber 56 to the intermediate chamber 58, with any surplus
fluid escaping to the return tank through the connection 26,28. Thus, the
piston system will be moved into a bottom position, in which the top edge
46 of the upper piston 44 will cause the stub 42 to be opened to the upper
cylinder space 54. By this connection the medium pressure in that chamber
will gain access to the pilot pipe 38 and thereby cause a shifting of the
control unit into its "working stroke" condition, in which it connects the
inlet branch 36 to the pipe 22, whereby the medium pressure fluid is
supplied to the lower piston chamber 56 while the pipe 20 is connected
only to the outlet 26,28. The medium pressure fluid thus acting on the
bottom side of the broad piston 52 will force the piston system upwardly,
whereby the narrower upper piston 44 produces a substantially higher
pressure in the chamber 54 and therewith in the outlet pipe 14; hence the
desired pressure amplification. When the piston system is forced upwardly
to the point where the lower piston edge 48 registers with the stub 42 the
situation will be changed, as the pilot pipe 38 will then be connected to
the low pressure chamber 58 between the two pistons. Hereby the control
unit 24 is switched back into its "return" mode, governed by the action of
the spring 32, whereby the connection between the pipes 20 and 22 will be
reestablished and the piston system will be allowed to be forced down by
the intermediate pressure acting upon the upper piston surface 46.
In principle the system thus described will work perfectly by reciprocating
the piston system so as to maintain a high pressure on the outlet pipe 14,
and the system described is rather simple in utilizing the piston 44
directly as a control valve member for changing the control pressure in
the pilot line 38 according to the upper or lower positioning of the
piston system.
The piston spring 60 is designed such that it will allow the piston system
44,52 to be pressed fully down only when the medium pressure, as
introduced through the conduit 10, is sufficiently high to effect
compression of the spring 32 in the slide controller 24. Thus, the system
will stop whenever the pressure at the inlet 4 is not sufficient to
condition a safe operation of the system.
The control unit 24 is shown in more detail in FIGS. 2-5. It comprises a
cylindrical outer housing or first slide valve member 64 having an axial
bore 66, in which a cylindrical inner slide 68 is arranged, consisting of
an outer slide or second valve member 70 and an inner, auxiliary slide 72.
The latter is in frictional engagement with inside of the slide 70 by a
friction ring 74 mounted adjacent the lower end of the slide 70, this end
being closed by means of a stopper 76, which abuts the upper end of the
spring 32 in the chamber portion 30.
The outer housing 64 has connector openings for the various conduits
36,20,22,34 and 38. The bottom chamber 30 has an upper shoulder portion 78
forming a stop for downward movement of the slide 70. At its upper end the
housing 64 is provided with an internal cylindrical recess 80, which takes
up a cross pin 82 mounted through an upper end portion of the interior,
tubular slide 72, so as to limit the axial movability of the interior
slide 72 to the displacement of the pin 82 between the upper and lower end
of the recess 80.
The slide 70 is shaped with an outer cylindrical recess 84, which, as shown
in FIGS. 2 and 5, is usable for the interconnection of the two conduits 20
and 22, while just above the upper end of this recess the slide 70 is
provided with an outer annular recess 86, which is open towards the inner
side of the slide through a number of radial bores 88. A similar recess
and bore system 90,92 is provided just below the lower end of the
cylindrical recess 84.
The central bore, 94, of the innermost tubular slide 72 is in open
connection with the upper chamber portion 40 of the housing 64, directly
or through radial holes 96 in the top end of the slide, and the bore 94 is
open at the bottom. In the outside of this auxiliary slide member there is
provided a cylindrical recess 98, at the top and bottom ends of which
there are arranged radial holes 100 connecting the central bore 94 with
the said recess 98.
FIG. 2 may represent a start situation, in which the piston system 44,52
assumes an upper position and the slide 68 in the control unit 24 also
assumes an upper position, biased by the spring 32, which urges the slide
system 70,72 upwardly so as to force the cross pin 82 against the top end
of the recess 80 in the upper end of the housing 64. The connector stub 42
and therewith the pilot conduit 38 is connected to the intermediate
cylinder chamber 58 and thereby to the return pipe 26, whereby the control
slide 68 is not subjected to any downwardly displacing pressure. In this
position the cylindrical outer recess 84 of the slide 70 forms a
connection between the conduits 20 and 22, i.e. between the opposite sides
of the lower piston 52, and the slide 70 closes the inlet from the medium
pressure branch pipe 36.
When a medium fluid pressure is applied to the main inlet 4 this pressure
will be supplied to the top chamber 54 of the cylinder 12, whereby the
piston system 44,52 is forced downwardly. The connector stub 42 is closed
by the descending piston 44, and the fluid in chamber 56 underneath the
lower piston 52 flows to the opposite chamber 58 through the recess 84 of
the control slide 70, while excess fluid will be pressed out through the
conduit 26 to the tank return outlet 28.
When the piston system 44,52 reaches a lower position, in which the top of
the high pressure piston 44 reaches the connector stub 42 the medium
pressure above the piston top will be transferred into the pilot conduit
38, whereby the medium pressure will act on the top end of the slide 68 so
as to press this slide downwardly until the cross pin 82 abuts the lower
end of the recess 80, see FIG. 3. In just that position the cylindrical
recess 84 has left its connection with the pipe 20 and established
connection between the pipe 22 and the supply pipe 36, i.e. the medium
pressure fluid may now intrude into the lower cylinder chamber 56 and
force the piston system upwardly in its said working stroke. The inner
cylindrical recess 98 is at its lower end connected with the groove and
hole system 90,92, whereby the central bore 94, through the holes 100, is
connected with the supply pipe 36. Should the piston 44 already have
closed the stub 42, medium pressure fluid will thus still be supplied to
the slide system, biasing the same downwardly.
For this reason, while the auxiliary slide 72 is stopped by the pin 82
engaging the lower end of the recess 80, the slide 70 will continue
downwardly, further compressing the spring 32, until it meets the lower
stop shoulder 78, see FIG. 4. This extra displacement of the slide does
not change the relative position of the recess 84, i.e. the working stroke
of the piston system may continue or proceed, but the position of the
inner recess 98 will be changed to the effect that it is closed towards
the supply pipe 36 and opened towards the pipe 20, i.e. only towards the
return system 22,26,28. Thus, the connection is no longer active, but it
already has fulfilled one of its purposes, that is, to amplify the
downward shifting movement of the slide system.
At the end of the working stroke of the piston system the lower piston end
48 will uncover the stub 42 more or less, whereby the pressure on the
slide system is relieved towards the common cylinder chamber 58 and the
return system 20, 26,28, i.e. now the spring 32 is able to force the slide
system upwardly, see FIG. 5. Initially the inner slide 72 will be brought
along by virtue of its frictional engagement with the outer slide 70 at
the friction ring 74, until the cross pin 82 abuts the upper end of the
recess 80. During this first phase of the shifting operation the central
bore of the slide system will be briefly connected, through holes 100,
recess 98, radial holes 88 and annular recess 86, with the return or low
pressure pipe 20, and it will be appreciated that this gives rise to an
extra and safe pressure relief of the inner pressure of the slide system,
i.e. an amplification of the pressure relieving function for ensuring a
safe switching of the slide system. Also, during the initial movement of
the slide system, the outer cylindrical recess will be disconnected from
the inlet pipe 36 and connected to the pipe 20, such that the return
connection from pipe 20 to pipe 22 is rapidly reestablished as in the
first instance, the medium pressure fluid will then be supplied to the
upper cylinder chamber 54 through the pipe 10 for effecting a quick
downstroke or return stroke of the piston system 44,52.
However, even if the stub 42 has now already been closed by the descending
piston 44, the spring 32 will be able to urge the outer slide 70 further
upwardly, viz. from FIG. 5 back to FIG. 2, until the upper radial holes 88
are closed for outflow of medium from the inner slide system, this
position being shown in FIG. 2. It will be noted that the latter
connection is closed even though the annular recess 86 is still open
towards the pipe 20. At the same time the corresponding connection between
the recess 98 and the lower radial holes 92 will be opened, though without
any effect because the associated annular recess 90 is closed outwardly.
The slide system now remains in this position while the working stroke of
the piston system goes on, just as described above, whereafter the
described cyclic operation will be repeated as long as the system is kept
working.
The inner or auxiliary slide 72 serves the important purpose of permitting
the discussed amplification functions in immediate response to each
initial shifting of the slide system, so as to stabilize the shifting, and
it is obtained automatically that this slide, after having performed that
action at each shifting, is pre-adjusted so as to be able to perform the
desired action immediately by the following shifting. It is well thinkable
that the same kind of operation could be achieved by servo controlled
switching means based on the use of appropriate sensors, but it will be
appreciated that in the preferred embodiment of the invention it is not at
all necessary to make use of such supplementary control means, which would
be bound to make the system more expensive. The auxiliary slide should not
necessarily operate by a relative movement in the axial direction, as it
might alternatively operate by a rotational movement.
Another important advantage of the described arrangement is that it will
not be required, anywhere in the system, to make use of quite narrow or
nozzle-like flow connections, so also for this reason the system will be
very reliable in operation. It is important that the return stroke of the
piston system is effected by the medium pressure flow being supplied to
the chamber 58, i.e. to the piston side having the smaller area due to the
rod 50. Hereby a relatively small amount of fluid is required for
displacing the piston, which promotes the desired rapidity of the return
stroke.
It should be mentioned as a special advantage that the pistons 44 and 52
are always forced against each other, such that the piston rod 50 should
merely act as a spacer rod, i.e. it is not required that the two pistons
be rigidly interconnected. Consequently, the two cylinder portions 12 and
18 will not have to be arranged exactly coaxially with each other, which
is of course also a significant advantage.
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